This invention relates to a sediment raking device for sedimentation tanks.
As is known, solids in slurries are separated from the liquid component of the slurry by sedimentation in thickeners the main parts of which are a settling tank for holding a generally quiescent pool of liquid, and slow-moving rakes trailed along the bottom thereof. The rakes are destined to urge settled sludge to a discharge sump. If the solid-liquid ratios of slurry inputs are uniform, the raking devices work dependably. Surges of solids, however, may result in localized solid deposits which impede the trailing motion of the rake blades. Then, the rakes may be damaged unless special steps are taken.
It has been suggested to meet such difficulties by coupling the rake arms to the shaft of their rotation by universal joints so that in response to overload the rake arms pivot upwardly about a horizontal axis and reerward about a vertical axis of their universal joint. The lifted arms shave the deposit and, upon subsequent passes, wear it away.
Such sediment raking device is described in U.S. Pat. No. 3,833,126 which gives a full account of the parts of such and their various functions. Therefore, the prior specification is hereby incorporated by reference.
With the known suggestion, the rake arms have their inner ends pivotally connected to the lower end of a centrally disposed torque tube or cage. Thus, when a rake arm encounters a large solids accumulation, or overload, resistance increases, the raking arm pivots about its pin upward and back thereby reducing its bite into the sludge.
However, the rake arms which work in the manner of single-arm levers may bend due to their own weights and may flex when they encounter an obstacle. Overloads will occur particularly when in the proximity of the axis of raking arm rotation sludge accumulates and causes the raking arms to be lifted at relatively short arms while their greater length is without support and their pivotal connections with the torque tube are loaded by shearing forces.